Effects of pea (Pisum sativum) genotypes and Rhizobium leguminosarum strains on N2(C2H2) fixation and growth

Factors affecting the efficiency of selection for increased N2(C2H2) fixation in Pisum sativum L. were examined. Ten genotypes, previously selected for variability in fixation rates when inoculated with commercial (mixed strain) Rhizobium leguminosarum, were examined using pure strain (128C52 and 10004) inocula. Strains and genotypes both affected fixation rates, but genotype × strain interaction was also found. Increases in relative growth rate (RGR) were associated with increases in fixation across strains but not with increases in fixation across genotypes. These differences in the response to changes of strain and genotype were further studied over a 4-week period using genotypes specifically selected for high or low rates of C2H2 reduction with both strains. Strain 128C52 and the genotypes selected for high rates of C2H2 reduction produced greater maximum rates of C2H2 reduction than their low counterparts, but the strains also differed in the time at which fixation began. Plants inoculated with stra...